RE: [RFC PATCH 0/4]: affinity-on-next-touch

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Thu, 2009-06-18 at 00:37 -0400, Lee Schermerhorn wrote:
> On Wed, 2009-06-17 at 09:45 +0200, Stefan Lankes wrote:
> > > I've placed the last rebased version in :
> > > 
> > > http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.28-rc4-mmotm-
> > > 081110/
> > > 
> > 
> > OK! I will try to reconstruct the problem.
> 
> Stefan:
> 
> Today I rebased the migrate on fault patches to 2.6.30-mmotm-090612...
> [along with my shared policy series atop which they sit in my tree].
> Patches reside in:
> 
> http://free.linux.hp.com/~lts/Patches/PageMigration/2.6.30-mmotm-090612-1220/
> 

I have updated the migrate-on-fault tarball in the above location to fix
part of the problems I was seeing.  See below.

> 
> I did a quick test.  I'm afraid the patches have suffered some "bit rot"
> vis a vis mainline/mmotm over the past several months.  Two possibly
> related issues:
> 
> 1) lazy migration doesn't seem to work. Looks like
> mbind(<some-policy>+MPOL_MF_MOVE+MPOL_MF_LAZY) is not unmapping the
> pages so, of course, migrate on fault won't work.  I suspect the
> reference count handling has changed since I last tried this.  [Note one
> of the patch conflicts was in the MPOL_MF_LAZY addition to the mbind
> flag definitions in mempolicy.h and I may have botched the resolution
> thereof.]
> 
> 2) When the pages get freed on exit/unmap, they are still PageLocked()
> and free_pages_check()/bad_page() bugs out with bad page state.
> 
> Note:  This is independent of memcg--i.e., happens whether or not memcg
> configured.
> 
<snip>

OK.  Found time to look at this.  Turns out I hadn't tested since
trylock_page() was introduced.  I did a one-for-one replacement of the
old API [TestSetPageLocked()], not noticing that the sense of the return
was inverted.  Thus, I was bailing out of the migrate_pages_unmap_only()
loop with the page locked, thinking someone else had locked it and would
take care of it.  Since the page wasn't unmapped from the page table[s],
of course it wouldn't migrate on fault--wouldn't even fault!

Fixed this.

Now:  lazy migration works w/ or w/o memcg configured, but NOT with the
swap resource controller configured.  I'll look at that as time permits.

Lee